An infusion system can be as simple as a needle and syringe or as complex as a catheter, port reservoir, Huber needle, jacket, tether, swivel, swivel holder, extension lines and pump. Just as the proper sized needle and appropriate volume syringe are necessary to achieve a simple IV injection, more complex systems also require the selection of components that best suit the infusion. Both complex and simple systems will function perfectly as quality infusion systems, but optimally, only under the right circumstances

When a researcher contacts us to determine which infusion system would be most suitable for their applications, they must first answer a number of questions relating to their unique requirements. The answers to these questions will dictate what components should be used to achieve their research objectives. In this section we will take you through these questions in detail, and explain how the answers affect the target system. By asking yourself these questions, finding the answers and understanding how they will affect your choices, you will be able to design your own systems with the components in Section 1 (products).

What is the intended species?

The main differences between species, as they pertain to infusion system design, are the variations in size and anatomy. The size of the animal, and therefore the vessel or other access site, varies greatly with species. One of the components most affected by these size variations is the catheter. In relatively small animals, such as a rat or mouse, the vessels and other potential administration sites can be extremely small so a catheter with a small outer diameter (OD) must be used. For example, the femoral vein of a 200 gram rat will accept a catheter with an OD of .040 inches. Smaller catheters will fit more easily however too small a catheter may restrict flow or allow even a small fibrin plug to stop flow altogether. The length of the catheter also must be adjusted to account for the distance between where the tip is to reside and the cutaneous exit site (or subcutaneous port reservoir). (note: SAI has streamlined the process finding the right catheter for the right animal and vessel by designing catheters that are species and site specific).

Test formulations can be infused by many routes at many sites. The most common route of infusion is intravenous but intrathecal, epidural, subcutaneous, intracerebral ventricular, intraduodenal among others, are also used. The determination of the route of administration depends on many factors related to the test article and formulation. How the test article is absorbed, distributed, metaboltized and excreted play a major role in this determination. Pharmacologic effect as well physical and chemical characteristics of the formulation also may have a direct influence. For the most part, discussions here will focus on administration of intravenous solutions.

As a rule, whenever possible, all solutions intended for IV infusion should be adjusted for both pH and tonocity prior to infusion. Solutions with very high or very low pH’s can cause serious local irritation. Solutions that are very hypotonic or hypertonic may not be hemocompatible and may also cause serious complications.

The choice between an ambulatory or tethered infusion system became possible when infusion pumps that were small, accurate and rugged enough to accomplish this feat became available. Prior to then, tethered systems using volumetric or syringe driver pumps were necessary.

Ambulatory systems allow animals unrestrained and untethered freedom of movement at all times.  Long-term tethered infusion in large animals has been banned in some European countries due to the belief that untethered systems put less stress on the animal subjects. New advancements in pump technology, jacket design, catheter material, and surgical techniques and the improved demeanor of the animals, have made this the system of choice for many researchers.

First and foremost the material chosen for infusion catheters must be compatible with the infusate. Information regarding material compatibility can be found. The polymers most often used in preclinical and clinical practice are silicone, polyurethane (PU), polyethylene (PE), polyvinylchloride (PVC), Teflon (PTFE), and nylon. Flexibility, durability, chemical compatibility, biocompatibility and thrombogenicity are the characteristics to evaluate when choosing between them. Silicone and PU are the two most often used for IV infusion based on these criteria.

The importance of the technical staff involved in the surgical, maintenance and animal care procedures can not be overly stressed. Not only are the training and skill of these staff of the utmost importance but also their professional experience and personal preferences.